The Relationship of Vegetation to Methane Emission and Hydrochemical Gradients in Northern Peatlands

Abstract

1 The bryophyte and vascular flora were described for a range of forested and open peatlands in the mid-boreal Clay Belt region of Canada, and in the subarctic region of the Labrador Trough, Quebec. The floristic patterns and their relationships to methane (CH4) emission, hydrology and water chemistry were analysed with classification (TWINSPAN), detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA). 2 Despite differences in vegetation physiognomy, chemistry, and geology, water chemistry (pH, Ca, Mg, Kcorr) and hydrology explain most of the species distribution in both peatland regions. In the Clay Belt, bryophytes respond primarily to water table position, and secondarily to water chemistry; the reverse is true for the vascular flora. The bryophyte and vascular ordinations are more similar to each other in the Labrador Trough than in boreal sites. 3 Although CH4 emissions are lower in subarctic than in boreal sites, mean CH4 flux is strongly correlated with mean water table position (r2 = 0.73) in both regions, but is not correlated with water chemistry. The highest CH4 emissions (seasonal mean > 100mg m-2 day-') occur in raised bog and patterned poor fen pools where the peat mat is degrading. 4 The relationships among CH4 flux, mean water table position, and species distribution are similar in both boreal and subarctic regions. Bryophytes are generally better predictors of CH4 flux than vascular plants, except for certain species in flooded sites (e.g. Carex spp.). Bryophytes are also better indicators of the long-term average position of the water table, reflecting relative zones of methane production and oxidation over the season. In the vascular plant analyses, shrub cover indicates dry conditions and low CH4 flux in the sharply differentiated string-flark-pool topography of the subarctic fens, but is less predictive of CH4 emission in the drier hummockhollow microtopography at boreal sites where shrubs and trees are more pervasive. Overall herbaceous or sedge cover is not indicative of CH4 flux in either region.